Optical wavelengths are an alternative to radio-frequency links for future satellite-to-ground transmissions. They are envisioned in the framework of payload/telemetry data transfer (optical downlinks from LEO satellites) or communication (bi-directional optical links with GEO satellites). However, as it propagates through the atmosphere, the optical wave can be deeply affected by atmospheric turbulence which induces randomspatial and temporal variations of its amplitude and phase. Variations in amplitude translate into fluctuations of the collected power (scintillation). The phase distortions affect the spatial distribution of the power at the focal plane of the telescope causing deleterious losses when the incident flux needs to be coupled to an optoelectronic detector or to a single-mode optical fiber. Such losses result in dynamical attenuations of the received signal -called fading- and hence potentially to the loss of information. The most recent feasibility studies highlight the use of two types of fading mitigation techniques : adaptive optics systems and digital techniques (coding and interleaving). To limit the complexity and cost of such systems, the optimization of these mitigation techniques should be conducted jointly. The main objective of this thesis is therefore the investigation of the complementarity of physical (adaptive optics) and digital data reliability mechanisms (interleaving, correcting and erasure codes in a cross-layer approach).

This paper studies the performance of the generalized likelihood ratio test (GLRT) for the conditional signal model. By conditional signal model, we mean that under both hypotheses, the observations are a linear superposition of unknown deterministic signals corrupted by additive noise, with a mixing matrix depending on an unknown deterministic parameter vector. The contribution of this work is the derivation of closed form expressions for the probabilities of false alarm and of detection of the GLRT at high signal-to-noise ratio, allowing the receiver operating characteristic of the GLRT to be computed analytically. The most general case is tackled, i.e., when the number of unknown signals and the number of unknown deterministic parameters of the mixing matrix are allowed to be different under the two hypotheses.

Les systèmes dits Sensor Webs sont des middlewares informatiques assurant la communication entre les capteurs et les applications. En tant que véritables médiateurs, la popularité de ces systèmes n’a cessé de grandir depuis l’apparition des tout premiers capteurs. Plus récemment, l’émergence de nouveaux paradigmes tels que l’Internet des Objets (IoT) a complètement révolutionné les systèmes basés sur les capteurs en général. Parmi eux, les Sensor Webs ne dérogent pas à cette règle et doivent maintenant répondre à de nouveaux défis, notamment en termes d’intégration, de Qualité des Observations (QoO) et d’adaptation système. Dans le cadre de ma thèse, j'ai proposé une nouvelle génération de Sensor Webs capables d’adapter la QoO distribuée de manière autonomique et spécifique à chaque application (QASWS). Premièrement, j'introduirai un framework générique destiné aux chercheurs et développeurs souhaitant concevoir leur propre solution QASWS. Dans un deuxième temps, je montrerai comment j'ai utilisé ce framework afin de développer une plateforme d’intégration pour l’évaluation de la QoO à la demande (iQAS). Après avoir évalué ses performances, je présenterai trois cas d’utilisation pour la plateforme iQAS. Finalement, je conclurai ma présentation en imaginant l’apport de certains paradigmes transverses vis-à-vis de la QoO dans un futur proche.

Les réseaux de capteurs type LPWAN (grande autonomie, grande couverture, faible débit) sont en plein essor. Ces réseaux, qui ont pour but de connecter des milliers de capteurs sans fils de la manière la plus efficace possible, seraient un maillon indispensable à l’internet des objets tel qu’il est imaginé dans les années à venir. Dans le but d’augmenter la couverture de ces services, un lien satellite est envisagé. Cette thèse étudie les contraintes liées à l’utilisation d’un lien satellite unidirectionnel dans un système terrestre étendu, sans modifications du matériel, supposé bas-coût. Après une rapide présentation du milieu de l’IoT et des solutions LPWAN terrestres, nous présenterons la solution et le système choisis, compatible LTE NB-IoT. L’utilisation d’un lien satellite limite le système en termes de bilan de liaison et d’interférences. On cherchera alors à quantifier ces interférences et à obtenir les performances d’un tel réseau.

For future satellite-to-ground communications link, very high throughput might be achievable at a reasonable cost assuming the use of existing single mode components developed for fiber technologies (optical detectors and amplifiers, MUX/DEMUX...). The influence of atmospheric turbulence degrades the injection efficiency of the incoming wave into single mode components. This leads to signal fading and channel impairments. Several mitigation strategies are considered to prevent them. The use of adaptive optics (AO) should contribute to reduce substantially the criticality of the fading at the expense of potentially complex and expensive systems if very high stability of the injection is requested. The use of appropriate numerical mitigation techniques (coding+interleaving) can help to relax the specifications and cost of AO systems but could lead among others to unmanageable buffer size. Thus the specification of AO correction and interleavers/forward error codes should be addressed jointly. A model to evaluate the channel capacity in terms of outage probability and packet error rate has been developed that jointly takes into account partial correction by AO and channel interleaving. It includes the capability to evaluate coded transmission performance over the correlated FSO channel in satellite-to-ground scenarios. This model is presented here and confronted to numerical simulations for several distinct correction cases. The interdependence of AO correction with numerical mitigation techniques is investigated.

Built upon the Internet of Things (IoT), the Internet of Everything (IoE) acknowledges the importance of data quality within sensor-based systems, alongside with people, processes and Things. Nevertheless, the impact of many technologies and paradigms that pertain to the IoE is still unknown regarding Quality of Observation (QoO). This paper proposes to study experimental results from three IoE-related deployment scenarios in order to promote the QoO notion and raise awareness about the need for characterizing observation quality within sensor-based systems. We specifically tailor the definition of QoO attributes to each use case, assessing observation accuracy within Smart Cities, observation rate for virtual sensors and observation freshness within post-disaster areas. To emulate these different experiments, we rely on a custom-developed integration platform for the assessment of QoO as a service called iQAS. We show that QoO attributes should be used to specify what is an observation of “good quality”, that virtual sensors may have specific and limiting capabilities impacting QoO and that network QoS and QoO are two complementary quality dimensions that should be used together to improve the overall service provided to end-users

The design of a new GNSS signal is always a trade-off between improving performance and increasing complexity, or even between improving different performance criteria. Position accuracy, receiver sensitivity (acquisition, tracking or data demodulation thresholds) or the Time-To-First-Fix (TTFF) are examples of those GNSS receivers performance criteria. Within the framework of Galileo 2nd Generation (G2G), adding a new signal component dedicated to aid the acquisition process on E1 can help to improve performance of GNSS receivers with respect to these criteria as it was shown in [1]. In order to create this new component, various aspects such as the spreading modulation, the data navigation content, the channel coding or the Pseudo-Random Noise (PRN) codes must be studied. To this end, this paper firstly proposes the study of new spreading modulations, and secondly, we investigate on PRN codes that can be well suited to the proposed Acquisition-Aiding signal.